The best replacement for kalman filter is hmm.

The best alternatives to kalman filter are rated as following:
★★★★★  hmm
★★★★  extended kalman filter
★★★★  hidden markov model
★★★  exponential smoothing
★★★  low pass
★★  particle filter
★★  complementary filter
★★  moving average
★  luenberger observer
★  least squares

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Speaking about kalman filter, one probably shouldn't forget about imu.

Other search terms related to kalman filter and their ratings are:
★★★★★ imu
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kalman filter
hmm
extended kalman filter